In numerous fields of application, and in particular telecommunications, electric or fiber optic cables are inserted into ducts. There is therefore a need to minimize the coefficient of friction between cables and the inside walls of ducts.
A first known solution appears in French patent FR 2 674 364. In that document, the core of the cable passes via a first extruder which applies a conventional sheath thereto, often made of polyethylene. The sheathed core then passes through a second extruder which applies a composite lubricant layer thereto, such as an alloy of silicone resin and polyethylene. The cable lubricated in that way then passes in conventional manner through a cooling vessel.
A second known solution appears in German patent application DE-44 10 456. As in the first document, that document provides for an extruder to cover the core of a cable with a sheath. At the outlet from that extruder there is disposed a coating chamber for applying granules of hard material to the still-hot sheath, which granules are designed to become detached when the cable is inserted in a duct. Finally, the coated cable passes through a cooling vessel.
In both of those two prior solutions, it is necessary to interpose additional equipment between the extruder that is designed to make the sheath and the cooling vessel. That gives rise to a major alteration of the manufacturing line.
In addition, the equipment for depositing the lubricant must be very close to the sheath extrusion head since otherwise it is not possible to control the thickness of the sheath properly. In any event, the additional equipment occupies non-negligible space and such an organization is not favorable for good control over the dimensions of the sheath.